“And the lord of that servant, being moved with compassion, released him, and forgave him the debt.”
But his lord was a compassionate man. And when he saw his servant's repentance he forgave him his debt and released him. It may of course be that his hope from this was that his servant had learned his lesson and would now out of gratitude be his servant for life. But that was only secondary. The prime grounds for the forgiveness of the debt was the compassionate nature of the king.
Not the emphasis on the relationship. ‘The lord of that servant.' The one was supremely superior to the other. He had total rights. Jesus clearly intends us to see him as signifying the Lord of all.